短脉冲激光刻蚀加工铜材料的机制

 利用数值模拟方法，研究波长1 064 nm、脉冲宽度介于1~20 ps的激光在刻蚀铜靶时，单次脉冲作用下非平衡场刻蚀和热平衡刻蚀两种机制的竞争过程。结果表明：随着脉冲宽度的增加，刻蚀过程由非平衡电荷分离场刻蚀占主导地位转变为热平衡刻蚀起主要作用，且脉冲宽度和激光峰值功率密度增大到一定程度后，各种电子加速机制在不同时刻开始突显，电子能量分布出现多峰结构。在能量密度为15 J/cm2的激光作用下，1和5 ps脉宽对应的非平衡场刻蚀深度分别为110和101 nm，10和20 ps脉宽分别为25和18 nm。     

Differential mobility analysis of nanoparticles generated by laser vaporization and controlled condensation (LVCC)

Silicon and iron aluminide (FeAl) nanoparticles were synthesized by a laser vaporization controlled condensation (LVCC) method. The particles generated by the laser ablation of solid targets were transported and deposited in the presence of well-defined thermal and electric field in a newly designed flow-type LVCC chamber. The deposition process of nanoparticles was controlled by the balance of the external forces; i.e., gas flow, thermophoretic and electrostatic forces. The size distributions of generated nanoparticles were analyzed using a low-pressure differential mobility analyzer (LP-DMA). The effect of synthesis condition on the size distribution was analyzed by changing the pressure of the carrier gas (20–200 Torr), the temperature gradient in the LVCC chamber (ΔT=0–190°C) and the electric field applied between the LVCC chamber plates (E=0–3000 V/m). It was found that electrostatic field was effective to selectively deposit small size nanoparticles (about 10 nm) with expelling large droplet-like particles.     

Observable dependence of fluctuation-dissipation relations and effective temperatures

We study the nonequilibrium fluctuation-dissipation theorem (FDT) in the glass phase of Bouchaud's trap model. We incorporate an arbitrary observable m and obtain its correlation and response functions in closed form. A limiting nonequilibrium FDT plot is approached at long times for most choices of m. In contrast to standard mean field models, however, the shape of the plot depends nontrivially on the observable, and its slope varies continuously even though there is a single scaling of relaxation times with age. Nonequilibrium FDT plots can therefore not be used to define a meaningful effective temperature T(eff) in this model. Consequences for the wider applicability of an FDT-derived T(eff) are discussed.     

Upper bound for the magnetic force gradient in graphite

In this work we investigate possible ferromagnetic order on the graphite surface by using magnetic force microscopy (MFM). Our data show that the tip-sample interaction along the steps is independent of an external magnetic field. Moreover, by combining kelvin probe force microscopy and MFM, we are able to separate the electrostatic and magnetic interactions along the steps obtaining an upper bound for the magnetic force gradient of 16 μN/m. Our experiments suggest the absence of ferromagnetic signal in graphite at room temperature.     

电场作用下过冷水形核的分子动力学模拟

采用分子动力学模拟的方法研究了过冷水的结构和形核过程随电场强度变化的情况。对系统微观结构的分析显示在电场强度为0～10~(10)V/m范围内,处于200K的过冷水在5 ns时间内不足以发生形核,只有当电场强度增加到10~(11) V/m或者温度降低到100K时系统才能在5 ns内发生形核。模拟结果表明电场强度的改变对系统中水分子团簇的微观结构有明显影响,电场强度的增加能促进系统的短程有序性。     

Microwave-mediated heat transport in a quantum dot attached to leads

The thermoelectric effect in a quantum dot (QD) attached to two leads in the presence of microwave fields is studied by using the Keldysh nonequilibrium Green function technique. When the microwave is applied only on the QD and in the linear response regime, the main peaks in the thermoelectric figure of merit and the thermopower are found to decrease, with the emergence of a set of photon-induced peaks. Under this condition the microwave field cannot generate heat current or electrical bias voltage. Surprisingly, when the microwave field is applied only to one (bright) lead and not to the other (dark) lead or the QD, heat flows mostly from the dark to the bright lead, almost irrespective of the direction of the thermal gradient. We attribute this effect to microwave-induced opening of additional transport channels below the Fermi energy. The microwave field can change both the magnitude and the sign of the electrical bias voltage induced by the temperature gradient.     

Probing magnetic fields on crystals of the nanomagnet Mn12-acetate by electron paramagnetic resonance

We report on electron paramagnetic resonance (EPR) probing of magnetic fields and magnetic field gradients near the surface of a single crystal of the nanomagnet [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-Ac). As the EPR probe, we utilized a 0.7 mm x 30 microm x 30 microm fibrous needle of the organic conductor N-methylphenazinium-tetracyanoquinodimethane (NMP-TCNQ), which yields an exceptionally sharp peak, with a 0.2 G (approximately 20 microT) width. In the presence of Mn12-Ac, the probe's peak exhibits splitting on temperature lowering, which depends on the orientation of the Zeeman field relative to the axis of easy magnetization of the employed Mn12-Ac crystal. The shifted peaks yield the magnitude of the magnetic field from Mn12-Ac crystal to which the various fibers of the probe are subjected. In conjunction with electron microscopy, the shifts yield the field gradient at the crystal surface and its change with temperature. For Mn12-Ac at 10 K, the surface magnetic field was measured to be in the mT range and its gradient on the order of 50 T/m.     

Controlling Josephson transport by manipulation of Andreev levels in ballistic mesoscopic junctions

We discuss how to control dc Josephson current by influencing the structure and nonequilibrium population of Andreev levels via external electrostatic gates, current injection and electromagnetic radiation. In particular we will consider the ‘giant’ Josephson critical current in ‘long’ SIS tunnel junctions and the regular and anomalous nonequilibrium Josepson currents in three terminal SNS junctions. We will briefly discuss applications to the Josephson field effect transistor (JOFET) and to the newly invented Josephson interference transistor (JOINT).     

Instability of a bubble in a liquid dielectric in an external electrostatic field

The sizes, charges, and number of daughter bubbles emitted during the development of instability with respect to the polarization charge in a uniform electrostatic field of a gas bubble in a liquid dielectric are found on the basis of the Onsager principle of minimum energy dissipation for nonequilibrium processes. Zh. Tekh. Fiz. 69, 10–13 (November 1999)     

Nonequilibrium quantum meson gas: Dimensional reduction

A nonequilibrium quantum gas of interacting relativistic effective mesons, ressembling qualitatively those produced in a heavy-ion collision, is described by a scalar quantum field in (1 + 3) -dimensional Minkowski space. For high temperature and large temporal and spatial scales, we justify that classical statistical mechanics including quantum renormalization effects describe approximately the gas: nonequilibrium dimensional reduction (NEDR). As a source of hints, we treat the gas at equilibrium in real-time formalism and obtain simplifications for high temperature and large spatial scales, thereby extending a useful equilibrium dimensional reduction known for the imaginary-time formalism. By assumption, the nonequilibrium initial state of the gas, not far from thermal equilibrium, includes interactions and inhomogeneities. We use nonequilibrium real-time generating functionals and correlators at nonzero temperature. In the NEDR regime, our arguments yield: 1) renormalized correlators simplify, 2) the perturbative series for those simplified correlators can be resummed into a new nonequilibrium generating functional, Z’ _{r, dr} , which is super-renormalizable and includes renormalization effects (large position-dependent thermal self-energies and effective couplings). Z’ _{r, dr} could enable to study nonperturbatively changes in the phase structures of the field, by proceeding from the nonequilibrium quantum regime to the NEDR one.     

On the Physical Origin of Long-Ranged Fluctuations in Fluids in Thermal Nonequilibrium States

Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.     

Electrostatic field enhancement of Al(111) oxidation

We show that the electrostatic charging of an aluminum oxide film by electron-bombardment produces a greatly enhanced rate of Al(111) oxidation by O2(g) at 90 K, compared to a film which has not been bombarded by electrons. This novel memory effect for prior electron irradiation is caused by the negative electrostatic potential created and stored on the outer oxide film surface as a result of electron bombardment. The high electrostatic field ( approximately 10(7) V/cm) produced across the depth of the film is postulated to cause an enhancement of ion migration through the film, leading to rapid oxide film growth, as predicted by the Cabrera-Mott theory of low temperature metal oxidation.     

Water self-diffusion in Chlorella sp. studied by pulse field gradient NMR

The water self-diffusion behavior in chlorella water suspension was investigated by pulsed field gradient NMR technique. Three types of water was determined, which differs according to the self-diffusion coefficients; bulk water, extracellular and intracellular water. Intracellular and extracellular water self-diffusion were restricted, and the sizes of restriction regions were 3.4 microm and 17 microm, respectively. The water molecular exchange process between these three diffusion regions was investigated. The residence time and exchange rate constant for chlorella cells were obtained. The cell wall permeability determined from the rate constant as 3 x 10(-6) m/s agreed with the permeability 10(-6) m/s obtained from time dependence of intracellular water self-diffusion coefficient. The structural cluster model of chlorella cell is estimated to describe the extracellular water self-diffusion in chlorella water suspension.     

Thermomolecular orientation of nonpolar fluids

We investigate the response of molecular fluids to temperature gradients. Using nonequilibrium molecular dynamics computer simulations we show that nonpolar diatomic fluids adopt a preferred orientation as a response to a temperature gradient. We find that the magnitude of this thermomolecular orientation effect is proportional to the strength of the temperature gradient and the degree of molecular anisotropy, as defined by the different size or mass of the molecular atomic sites. We show that the preferred orientation of the molecules follows the same trends observed in the Soret effect of binary mixtures. We argue this is a general effect that should be observed in a wide range of length scales.     

Electrocaloric effect in triglycine sulfate under equilibrium and nonequilibrium thermodynamic conditions

The direct and indirect measurements of intensive electrocaloric effect in a triglycine sulfate ferroelectric crystal are performed under equilibrium and nonequilibrium thermodynamic conditions implemented in the adiabatic calorimeter. The effect of the electric field parameters (frequency, profile, and strength) on the value of the effect and degree of its reversibility are studied. The difference between the temperature variation values in a switched-on and switched-off dc field under quasi-isothermal conditions is established. The low-frequency periodic electric field induces the temperature gradient along the electrocaloric element and heat flux from its free end to the thermostated base. A significant excess of the field switching-off rate over the switching-on rate leads to a noticeable intensification of the cooling effect.     

Electric dipole moment calculations of molecules with sixteen valence electrons

The field gradient fluctuation at the Li⁺ nucleus in dilute aqueous solution is calculated via Monte Carlo simulations of Li⁺ + nH₂O clusters (n = 6, 50 and 150). The intermolecular potentials and the lithium field gradient function, necessary for the simulations, are based on ab initio quantum mechanical calculations. It is found that the dominant contribution to the field gradient fluctuation at the lithium nucleus comes from the water molecules in the first shell. Furthermore, it is the lateral displacement of these molecules that causes the largest fluctuation. The contribution from the rotation of a water molecule is of minor importance. The field gradient at a lithium nucleus arising from a water molecule is badly described in a simple electrostatic model.     

Fourier's law from closure equations

We sketch a rigorous derivation of Fourier's law from a system of closure equations for a nonequilibrium stationary state of a Hamiltonian system of coupled oscillators subjected to heat baths on the boundary. The local heat flux is proportional to the temperature gradient with a temperature dependent heat conductivity and the stationary temperature exhibits a nonlinear profile.     

Elastic displacement of surface due to laser picosecond pulse heating of gold

Laser picosecond pulse heating initiates nonequilibrium energy transport in the surface vicinity of the metallic substrates. In this case, electron temperature rises rapidly while lattice site temperature is slow during the heating period. Although the rise of lattice site temperature is low, the temperature gradient is high. This results in elastic displacement of the surface. To model the heating process thermomechanical coupling needs to be introduced in the analysis. In the present study, picosecond pulse heating of gold surface is considered. Three-dimensional analysis of electron kinetic theory is introduced when formulating the electron and the lattice site temperatures. The analysis is extended to include the thermomechanical coupling due to mechanical response of the substrate material. The lattice site temperatures obtained from the electron kinetic theory are compared with the predictions of the two-equation model. It is found that both models predict almost identical temperature profiles in the surface vicinity of the substrate material. In addition, the surface displacement on the order of 10⁻¹¹ m is predicted.     

Long-range order and dynamic structure factor of a nematic under a thermal gradient

We use a fluctuating hydrodynamic approach to calculate the orientation fluctuations correlation functions of a thermotropic nematic liquid crystal in a nonequilibrium state induced by a stationary heat flux. Since in this nonequilibrium stationary state the hydrodynamic fluctuations evolve on three widely separated times scales, we use a time-scale perturbation procedure in order to partially diagonalize the hydrodynamic matrix. The wave number and frequency dependence of these orientation correlation functions is evaluated and their explicit functional form on position is also calculated analytically in and out of equilibrium. We show that for both states these correlations are long-ranged. This result shows that indeed, even in equilibrium there is long-range orientational order in the nematic, consistently with the well known properties of these systems.We also calculate the dynamic structure of the fluid in both states for a geometry consistent with light scattering experiments. We find that as with isotropic simple fluids, the external temperature gradient introduces an asymmetry in the spectrum shifting its maximum by an amount proportional to the magnitude of the gradient. This effect may be of the order of 7 per cent. Also, the width at half height may decrease by a factor of about 10 per cent. Since to our knowledge there are no experimental results available in the literature to compare with, the predictions of our model calculation remains to be assessed.     

Integral relations for the heat and mass transfer resistivities of the liquid–vapor interface

We derived integral relations for the heat and mass transfer resistivities of the liquid–vapor interface in a one-component system. These relations were obtained assuming the validity of the standard expression for the local entropy production rate as the product of the measurable heat flux times the gradient of the inverse temperature through the surface. The integral relations will be useful to interpret results from nonequilibrium molecular dynamics simulations. We verified in this paper that earlier results obtained using the nonequilibrium van der Waals square gradient model are reproduced. For this case, we calculated the Kapitza length along the coexistence curve.